Architecture
A bit of architecture
During the keynote speech at E3 AMD announced and named the 7nm NAVI based graphics cards the Radeon RX 5000 series products. AMD considers Navi to be a completely new architecture. No longer would it be GCN based, but rather RDNA (Radeon DNA). RDNA uses redesigned Compute Units, which should increase per-clock performance and efficiency. This also includes a new cache structure. The changes are said to boost performance by at least 25 percent per cycle ("IPC") seen from Vega and increase efficiency (wattage) by at least 50 percent. According to AMD, the Navi architecture will serve as the foundation for video cards for gamers in the coming years. Navi will be born and named as Radeon RX 5700 series, with the Radeon RX 5700 and 5700 XT series released initially. The NAVI architecture also will make its way into the Next-gen PlayStation, based on Zen2 and NAVI. NAVI is based on 7nm RDNA architecture (Radeon DNA).
Radeon DNA (rDNA)
AMD emphasizes strongly that with the introduction of rDNA, a new architecture has been implemented. It is the foundations of an architecture for the years to come, a new base building block for future designs as I like to refer to it. In its current form, I'd say it is a new more efficient shader architecture. One of the bigger changes compared to GCN is a new cache structure. By placing just the right amount of cache/buffers at different levels, more data throughput can be optimally moved to all key locations within the chip. The chip designer makes a comparison similar to the difference between Zen and Bulldozer. The reality is that NAVI in its current form is new in architecture, but shares minor design elements of GCN. The compute units have been overhauled though and we indeed agree and say, this is a new architecture. AMD mentioned RDNA has been specially developed with PC gaming in mind. AMD RDNA would offer 25% better performance per clock, and 50% better performance per watt. The strong focus overall was to increase IPC and then in specific on a single thread.
The graphics processor has 40 compute units, I personally always refer to these as shader clusters. Each cluster holds 64 shader units, also called stream processors. These compute units are connected to each other in pairs in a block. Per block 128 kB L1 cache is shared. If you look at the block diagram, edges of the chip show several L2 blocks. Over the GPU 4 MB L2 cache is shared. This functions as a cache buffer for external memory. Not to confuse with system memory, that would be the GDDR6 ICs connected to the memory controllers accumulating towards a 256-bit wide connection.
Each shader cluster as mentioned before holds 64 shader processors. That's similar to the previous GCN architecture in absolute numbers. However, in GCN they were divided into four blocks of 16. This has been rearranged for rDNA with two blocks of 32. That last bit (more energy efficient and a smaller design allows more transistors) also leans on the fact that they came from 12/14nm moving towards 7nm. RDNA would see a more 'pure' appearance in Navi 20. As mentioned before, ‘Big Navi’, a chip that will not likely be on the market until next year. We do expect to see hardware accelerated Raytracing in NAVI 20, but time will tell.
Navi's main architectural design 40 Shader clusters (CU) each CU 64 stream processors which tally up towards 2,560 stream processors for this generation of NAVI. NAVI shows to have four render-backends per shader clusters that totals up towards 64 ROPs. Which definitely is going to help out. Game performance in absolutes is stated to be close to 10 FLOPS single precision for the fully enabled GPU (XT), which is not bad.
Display and video/media engine
Radeon series 5700 obviously will support FreeSync 2 (Dolby Vision HDR10). Connectivity wise you'll notice that the mini USB connector for VR is not there, that's optional to offer for the AIB partners. But it does confirm what I have been saying a long time, the VR trend has passed. You'll notice HDMI 2.0b support (not 2.1), new is Display Stream Compression which we'll talk a bit more about in the actual review. The media engine has been updated as well, now offering support for H.264 4K150/8K30 Decodes and 4K90 Encodes (that's Ultra HD recording at 90 Hz/PS). For H.265 you'll see 4K60 Decode support, 4K90 Encode support. lastly, Vp9 has become more popular with Youtube and Twitch supporting it and as such, that was bumped up towards 4K60 Decodes. The new Navi cards support both HDR10 and Dolby Vision.
